This invention relates to a method for preparation of carbamate compounds. In particular, the present invention relates to the use of a certain class of catalysts to increase the rate of carbamate compound formation while greatly decreasing the rate of by-product formation.
Carbamate compounds are a commercially important class of organic compounds. Carbamates are useful as intermediates in the synthesis of a wide variety of organic compounds, such as microbicides, agricultural pesticides and pharmaceutical agents. Many carbamate compounds are themselves known as microbicides, agricultural pesticides and pharmaceutical agents.
Carbamate compounds may be prepared by a variety of methods. Such methods include the reaction of an amide in the presence of an alcohol with a suitable catalyst, the reaction of alcohols with cyanogen halide, the reaction of alkyl hypochlorites with isonitriles, the reaction of haloformates with amines, and the reaction of isocyanates with either oximes or alcohols. Commercially important methods of preparing carbamate compounds are those involving isocyanates. These isocyanate preparations typically require the use of catalysts, such as metal salts, for the reaction to proceed at all and usually result in the presence of significant levels of by-products in the carbamate produced. Much cost and effort must then be spent to purify the resulting carbamate compound.
EP 824 862 A (Hsu et al.) discloses the preparation of certain dihaloformaldoxime carbamates by reacting certain dihaloformaldoximes with suitable isocyanates in the presence of a catalytic amount of dibutyltin dilaurate. While this type of reaction gives the desired carbamates, it is slow, produces low yields and results in a significant amount of by-products. This patent application neither teaches nor discloses other specific catalysts.
EP 014 032 A (Brand et al.) discloses the preparation of iodopropynyl carbamates by reacting an alkynol with an isocyanate, optionally in the presence of a catalyst, followed by iodination. Organic and inorganic basic compounds as well as soluble salts of metals are mentioned generally as possible catalysts. This publication does not disclose that certain catalysts are particularly effective in decreasing by-product formation during carbamate preparation.
There is thus a continuing need for methods of preparing carbamate compounds that are fast, provide high yields and produce very little by-products.